A bending tests of high strength aluminum alloy are carried out under hydrostatic pressure and with backup compression provided mechanically, and the stress and strain histories in the processes are calculated by the elastic-plastic FEM. The experimental results and the calculated results are used to study the fracture criteria. From the results, it becomes clear that the slip type fracture which occurs in bending with high backup compression using a small radius punch can be predicted by the criterion of a maximum shear stress, and the Oyane's criterion is successful in prediction of the critical punch strokes in bending in which the normal type fracture occurs. But the constants of Oyane's equation in bending do not agree with that in tensile test and in compression test.